The present application relates to a transistor suitable for being produced at a low temperature, a method of producing the transistor, and a display.
A field-effect transistor (FET) is used as a thin-film transistor (TFT) in many electronic units. The thin-film transistor is provided with a gate electrode, a gate insulating layer, a semiconductor layer, and a source electrode as well as a drain electrode on a substrate. According to the arrangement of the gate electrode of these elements, the thin-film transistors are broadly divided into two types of structure: top-gate type; and bottom-gate type. Also, according to the arrangement of the source electrode and the drain electrode, the thin-film transistors are divided into a top-contact type and a bottom-contact type.
For example, in the top-gate type TFT structure, the semiconductor layer, the gate insulating layer, the gate electrode, and the source/drain electrodes are provided in this order from the substrate side. In the bottom-gate type TFT structure, the gate electrode, the gate insulating layer, the semiconductor layer, and the source/drain electrodes are provided in this order from the substrate side. Currently, an inorganic substance such as silicon (Si) is often used as the semiconductor layer in such a TFT. However, an expensive large-scale unit is necessary in forming an inorganic semiconductor layer and therefore, development of lower-cost and simply-manufacturable TFTs has been desired.
One of such lower-cost TFTs is a TFT in which an organic semiconductor material is used for the semiconductor layer. Development of this type of TFT has been pursued vigorously. In forming a semiconductor layer with this organic semiconductor material, the organic semiconductor material is dissolved in an organic solvent, and then the organic solvent is dried from the applied resultant. Therefore, the organic semiconductor material enables to form a semiconductor layer at extremely low temperature, compared to the procedure in the past of forming an inorganic semiconductor layer made of amorphous silicon or the like. The organic semiconductor is allowed to be changed into an ink state. Therefore, it is possible to form an organic semiconductor layer in a low-temperature and easy production process by, for instance, coating deposition such as printing methods (see International Publication No. WO2003/016599, for example). In addition, this organic semiconductor layer is capable of being formed by drying an organic solvent having a low boiling point. Therefore, it is possible to produce this organic semiconductor layer at an extremely low temperature, as compared with a process of forming an inorganic semiconductor layer made of currently-available amorphous silicon or the like. This allows a plastic film or the like to be used, in place of a heat-resistant silicon substrate or glass substrate usually used, thereby making it possible to produce a flexible device.
It is also possible to control physical properties and performance of the organic semiconductor material, by designing the constituent molecules thereof. Moreover, the organic semiconductor layer is lighter than the inorganic semiconductor layer, and has flexibility. This organic semiconductor is likely to realize a low cost, high performance, flexibility, and weight reduction. Therefore, the organic semiconductor is expected to be used in organic light-emitting devices, and organic electronics devices such as organic solar battery, in addition to the TFTs (FETs).
Meanwhile, for the TFT using the organic semiconductor layer, forming layers other than the semiconductor layer at a low temperature has been also studied. Each of the electrodes is preferably made of metal, and is, for example, designed to obtain conductivity by dispersing silver nano-particles to an organic solvent to be in an ink state, and sintering the resultant at a low temperature (for example, about 150° C.). In addition, for each of the gate insulating layer and the like, an inorganic material such as silicon oxide (SiO2) employed in the TFT with the inorganic semiconductor layer is not used. Instead, a film formed by applying a polymer organic material being dissolved in a solvent is used for each of the gate insulating layer and the like. It is possible to form the insulating layer and the like in a low-temperature production process, without impairing the flexibility of the organic semiconductor.